@Tom: Fortunately, MacGoohan was carrying a tiny wire playback machine so he could hear it.

That reminds me of the old "Batman & Robin" film where batman is hanging from a rope ladder under the Bat Copter when a shark jumps out of the sea and attaches itself to Batman's leg ... and Batman shouts up to Robin "Pass me the Shark-Repellent Spray" -- and you see Robin in the cockpit reach for a rack containing four cans of sprak ... and sure enough one is marked "Shark Repellent" ... what are the odds?

My favorite episode of Patrick MacGoohan's Secret Agent (aka Danger Man, in the UK) was the one in which the secret message was recorded on the twisted wire used to hang a picture in the spy's apartment. Can't do that with magnetic tape! Fortunately, MacGoohan was carrying a tiny wire playback machine so he could hear it. (I never leave home without mine).

I had heard of wire recorders several decades ago when I've watched some of the old WWII movies. When they wanted to record something (surreptitiously) they always used a "wire recorder" complete with a bobbin of "wire". One advantage of wire over tape would be the environmental "extremes" that the wire could survive versus a tape.

@Set Square: If you are into Doctor Who, then if you ever find yourself in Bradford, yorkshire...

I've been into it ever since i saw the very first episode back in 1q963 when I was 6 years old!!! I'm from Sheffield, Yorkshire -- I occasionally get back to see my mom and little bro' -- the next time I'm over I will definately try to get over to Bradford to the National Media Museum (after which you can expect to see a follow-up blog) -- thanks for the suggestion!!!

@Set Square: If you want to see a comercial version of the the science museum in London UK did have one on display...

I last visited the London Science Museum in 2010 when I was speaking at the Embedded System Conference (I also got my picture taken standing next to the "Dr Who" style Police Box outside of Earl's Court Tube Station, but that's another story) ... but I don't recall seeing this in the museum ... maybe it' sjust a case of not knowing what I was looking at...